2.2 - community driven open source middleware

HornetQ REST Interface

2.2.2

iii

Preface ............................................................................................................................. v

1. Introduction ................................................................................................................. 1

1.1. Goals of REST Interface ..................................................................................... 1

2. Installation and Configuration ..................................................................................... 3

2.1. Installing Within Pre-configured Environment ........................................................ 3

2.2. Bootstrapping HornetQ Along with REST ............................................................. 4

2.3. REST Configuration ............................................................................................ 7

3. HornetQ REST Interface Basics .................................................................................. 9

3.1. Queue and Topic Resources ............................................................................... 9

3.2. Queue Resource Response Headers ................................................................. 10

3.3. Topic Resource Respones Headers ................................................................... 10

4. Posting Messages ..................................................................................................... 11

4.1. Duplicate Detection ........................................................................................... 12

4.2. Persistent Messages ......................................................................................... 14

4.3. TTL, Expiration and Priority ............................................................................... 15

5. Consuming Messages via Pull .................................................................................. 17

5.1. Auto-Acknowledge ............................................................................................ 18

5.1.1. Creating an Auto-Ack Consumer or Subscription ...................................... 18

5.1.2. Consuming Messages ............................................................................ 19

5.1.3. Recovering From Network Failures .......................................................... 21

5.1.4. Recovering From Client or Server Crashes .............................................. 21

5.2. Manual Acknowledgement ................................................................................. 22

5.2.1. Creating manually-acknowledged consumers or subscriptions ................... 22

5.2.2. Consuming and Acknowledging a Message ............................................. 24

5.2.3. Recovering From Network Failures .......................................................... 25

5.2.4. Recovering From Client or Server Crashes .............................................. 25

5.3. Blocking Pulls with Accept-Wait ......................................................................... 26

5.4. Clean Up Your Consumers! ............................................................................... 26

6. Pushing Messages ..................................................................................................... 29

6.1. The Queue Push Subscription XML ................................................................... 29

6.2. The Topic Push Subscription XML ..................................................................... 30

6.3. Creating a Push Subscription at Runtime ........................................................... 31

6.4. Creating a Push Subscription by Hand ............................................................... 32

6.5. Pushing to Authenticated Servers ...................................................................... 33

7. Creating Destinations ................................................................................................ 35

8. Securing the HornetQ REST Interface ....................................................................... 37

8.1. Within JBoss Application server ......................................................................... 37

8.2. Security in other environments ........................................................................... 37

9. Mixing JMS and REST ............................................................................................... 39

9.1. JMS Producers - REST Consumers ................................................................... 39

9.2. REST Producers - JMS Consumers ................................................................... 39

v

Preface

Commercial development support, production support and training for RESTEasy and HornetQ is

available through JBoss, a division of Red Hat Inc. (see http://www.jboss.com/).

Chapter 1.

1

IntroductionThe HornetQ REST interface allows you to leverage the reliability and scalability features of

HornetQ over a simple REST/HTTP interface. Messages are produced and consumed by sending

and receiving simple HTTP messages that contain the content you want to push around. For

instance, here's a simple example of posting an order to an order processing queue express as

an HTTP message:

POST /queue/orders/create HTTP/1.1

Host: example.com

Content-Type: application/xml

<order>

<name>Bill</name>

<item>iPhone 4</item>

<cost>$199.99</cost>

</order>

As you can see, we're just posting some arbitrary XML document to a URL. When the XML is

received on the server is it processed within HornetQ as a JMS message and distributed through

core HornetQ. Simple and easy. Consuming messages from a queue or topic looks very similar.

We'll discuss the entire interface in detail later in this docbook.

1.1. Goals of REST Interface

Why would you want to use HornetQ's REST interface? What are the goals of the REST interface?

• Easily usable by machine-based (code) clients.

• Zero client footprint. We want HornetQ to be usable by any client/programming language that

has an adequate HTTP client library. You shouldn't have to download, install, and configure a

special library to interact with HornetQ.

• Lightweight interoperability. The HTTP protocol is strong enough to be our message

exchange protocol. Since interactions are RESTful the HTTP uniform interface provides all the

interoperability you need to communicate between different languages, platforms, and even

messaging implementations that choose to implement the same RESTful interface as HornetQ

(i.e. the REST-* [http://rest-star.org] effort.)

• No envelope (i.e. SOAP) or feed (i.e. Atom) format requirements. You shouldn't have to learn,

use, or parse a specific XML document format in order to send and receive messages through

HornetQ's REST interface.

http://rest-star.org

http://rest-star.org

Chapter 1. Introduction

2

• Leverage the reliability, scalability, and clustering features of HornetQ on the back end without

sacrificing the simplicity of a REST interface.

Chapter 2.

3

Installation and ConfigurationHornetQ's REST interface is installed as a Web archive (WAR). It depends on the RESTEasy

[http://jboss.org/resteasy] project and can currently only run within a servlet container. Installing

the HornetQ REST interface is a little bit different depending whether HornetQ is already installed

and configured for your environment (i.e. you're deploying within JBoss 6 AppServer) or you want

the HornetQ REST WAR to startup and manage the HornetQ server.

2.1. Installing Within Pre-configured Environment

The section should be used when you want to use the HornetQ REST interface in an environment

that already has HornetQ installed and running, i.e. JBoss 6 Application Server. You must create

a Web archive (.WAR) file with the following web.xml settings:

<web-app>

<listener>

<listener-class>org.jboss.resteasy.plugins.server.servlet.ResteasyBootstrap</listener-class>

</listener>

<listener>

<listener-class>org.hornetq.rest.integration.RestMessagingBootstrapListener</listener-

class>

</listener>

<filter>

<filter-name>Rest-Messaging</filter-name>

<filter-class>

org.jboss.resteasy.plugins.server.servlet.FilterDispatcher

</filter-class>

</filter>

<filter-mapping>


<url-pattern>/*</url-pattern>

</filter-mapping>

</web-app

Within your WEB-INF/lib directory you must have the hornetq-rest.jar file. If RESTEasy is not

installed within your environment, you must add the RESTEasy jar files within the lib directory as

well. Here's a sample Maven pom.xml that can build your WAR for this case.

http://jboss.org/resteasy

http://jboss.org/resteasy

Chapter 2. Installation and C...

4

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/

XMLSchema-instance"

xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-

v4_0_0.xsd">

<modelVersion>4.0.0</modelVersion>

<groupId>org.somebody</groupId>

<artifactId>myapp</artifactId>

<packaging>war</packaging>

<name>My App</name>

<repositories>

<repository>

<id>jboss</id>

<url>http://repository.jboss.org/nexus/content/groups/public/</url>

</repository>

</repositories>

<build>

<plugin>

<groupId>org.apache.maven.plugins</groupId>

<artifactId>maven-compiler-plugin</artifactId>

<configuration>

<source>1.6</source>

<target>1.6</target>

</configuration>

</plugin>

</plugins>

</build>

<dependencies>

<dependency>

<groupId>org.hornetq.rest</groupId>

<artifactId>hornetq-rest</artifactId>

<version>2.2.0</version>

</dependency>

</dependencies>

</project>

2.2. Bootstrapping HornetQ Along with REST

You can bootstrap HornetQ within your WAR as well. To do this, you must have the HornetQ core

and JMS jars along with Netty, Resteasy, and the HornetQ REST jar within your WEB-INF/lib.

You must also have a hornetq-configuration.xml, hornetq-jms.xml, and hornetq-users.xml config

Bootstrapping HornetQ Along with REST

5

files within WEB-INF/classes. The examples that come with the HornetQ REST distribution show

how to do this. You must also add an additional listener to your web.xml file. Here's an example:

<web-app>

<listener>

<listener-class>org.jboss.resteasy.plugins.server.servlet.ResteasyBootstrap</listener-class>

</listener>

<listener>

<listener-class>org.hornetq.rest.integration.HornetqBootstrapListener</listener-class>

</listener>

<listener>

<listener-class>org.hornetq.rest.integration.RestMessagingBootstrapListener</listener-

class>

</listener>

<filter>


<filter-class>

org.jboss.resteasy.plugins.server.servlet.FilterDispatcher

</filter-class>

</filter>

<filter-mapping>


<url-pattern>/*</url-pattern>

</filter-mapping>

</web-app>

Here's a Maven pom.xml file for creating a WAR for this environment. Make sure your hornetq

configuration files are within the src/main/resources directory so that they are stuffed within the

WAR's WEB-INF/classes directory!

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/

XMLSchema-instance"

xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-

v4_0_0.xsd">

<modelVersion>4.0.0</modelVersion>

<groupId>org.somebody</groupId>


6

<artifactId>myapp</artifactId>

<packaging>war</packaging>

<name>My App</name>

<repositories>

<repository>

<id>jboss</id>

<url>http://repository.jboss.org/nexus/content/groups/public/</url>

</repository>

</repositories>

<build>

<plugin>

<groupId>org.apache.maven.plugins</groupId>

<artifactId>maven-compiler-plugin</artifactId>

<configuration>

<source>1.6</source>

<target>1.6</target>

</configuration>

</plugin>

</plugins>

</build>

<dependencies>

<dependency>

<groupId>org.hornetq</groupId>

<artifactId>hornetq-core</artifactId>

<version>2.1.1.GA</version>

</dependency>

<dependency>

<groupId>org.jboss.netty</groupId>

<artifactId>netty</artifactId>

</dependency>

<dependency>

<groupId>org.hornetq</groupId>

<artifactId>hornetq-jms</artifactId>


</dependency>

<dependency>

<groupId>org.jboss.spec.javax.jms</groupId>

<artifactId>jboss-jms-api_1.1_spec</artifactId>

<version>1.0.0.Beta1</version>

</dependency>

<dependency>

<groupId>org.hornetq.rest</groupId>

<artifactId>hornetq-rest</artifactId>

<version>2.2.0</version>

REST Configuration

7

</dependency>

<dependency>

<groupId>org.jboss.resteasy</groupId>

<artifactId>resteasy-jaxrs</artifactId>


</dependency>

<dependency>

<groupId>org.jboss.resteasy</groupId>

<artifactId>resteasy-jaxb-provider</artifactId>


</dependency>

</dependencies>

</project>

2.3. REST Configuration

The HornetQ REST implementation does have some configuration options. These are configured

via XML configuration file that must be in your WEB-INF/classes directory. You must set the

web.xml context-param rest.messaging.config.file to specify the name of the configuration

file. Below is the format of the XML configuration file and the default values for each.

<rest-messaging>

<server-in-vm-id>0</server-in-vm-id>

<use-link-headers>false</use-link-headers>

<default-durable-send>false</default-durable-send>

<dups-ok>true</dups-ok>

<topic-push-store-dir>topic-push-store</topic-push-store-dir>

<queue-push-store-dir>queue-push-store</queue-push-store-dir>

<producer-time-to-live>0</producer-time-to-live>

<producer-session-pool-size>10</producer-session-pool-size>

<session-timeout-task-interval>1</session-timeout-task-interval>

<consumer-session-timeout-seconds>300</consumer-session-timeout-seconds>

<consumer-window-size>-1</consumer-window-size>

</rest-messaging

Let's give an explanation of each config option.

server-in-vm-id

The HornetQ REST impl uses the IN-VM transport to communicate with HornetQ. It uses the

default server id, which is "0".


8

use-link-headers

By default, all links (URLs) are published using custom headers. You can instead have

the HornetQ REST implementation publish links using the Link Header specification [http://

tools.ietf.org/html/draft-nottingham-http-link-header-10] instead if you desire.

default-durable-send

Whether a posted message should be persisted by default if the user does not specify a

durable query parameter.

dups-ok

If this is true, no duplicate detection protocol will be enforced for message posting.

topic-push-store-dir

This must be a relative or absolute file system path. This is a directory where push registrations

for topics are stored. See Chapter 6.

queue-push-store-dir

This must be a relative or absolute file system path. This is a directory where push registrations

for queues are stored. See Chapter 6.

producer-session-pool-size

The REST implementation pools HornetQ sessions for sending messages. This is the size of

the pool. That number of sessions will be created at startup time.

producer-time-to-live

Default time to live for posted messages. Default is no ttl.

session-timeout-task-interval

Pull consumers and pull subscriptions can time out. This is the interval the thread that checks

for timed-out sessions will run at. A value of 1 means it will run every 1 second.

consumer-session-timeout-seconds

Timeout in seconds for pull consumers/subscriptions that remain idle for that amount of time.

consumer-window-size

For consumers, this config option is the same as the HornetQ one of the same name. It will

be used by sessions created by the HornetQ REST implementation.

http://tools.ietf.org/html/draft-nottingham-http-link-header-10



Chapter 3.

9

HornetQ REST Interface BasicsThe HornetQ REST interface publishes a variety of REST resources to perform various tasks on a

queue or topic. Only the top-level queue and topic URI schemes are published to the outside world.

You must discover all over resources to interact with by looking for and traversing links. You'll find

published links within custom response headers and embedded in published XML representations.

Let's look at how this works.

3.1. Queue and Topic Resources

To interact with a queue or topic you do a HEAD or GET request on the following relative URI

pattern:

/queues/{name}

/topics/{name}

The base of the URI is the base URL of the WAR you deployed the HornetQ REST server within as

defined in the Installation and Configuration section of this document. Replace the {name} string

within the above URI pattern with the name of the queue or topic you are interested in interacting

with. For example if you have configured a JMS topic named "foo" within your hornetq-jms.xml

file, the URI name should be "jms.topic.foo". If you have configured a JMS queue name "bar"

within your hornetq-jms.xml file, the URI name should be "jms.queue.bar". Internally, HornetQ

prepends the "jms.topic" or "jms.queue" strings to the name of the deployed destination. Next,

perform your HEAD or GET request on this URI. Here's what a request/response would look like.

HEAD /queues/jms.queue.bar HTTP/1.1

Host: example.com

--- Response ---

HTTP/1.1 200 Ok

msg-create: http://example.com/queues/jms.queue.bar/create

msg-pull-consumers: http://example.com/queues/jms.queue.bar/pull-consumers

msg-push-consumers: http://example.com/queues/jms.queue.bar/push-consumers

The HEAD or GET response contains a number of custom response headers that are URLs to

additional REST resources that allow you to interact with the queue or topic in different ways. It

is important not to rely on the scheme of the URLs returned within these headers as they are an

implementation detail. Treat them as opaque and query for them each and every time you initially

interact (at boot time) with the server. If you treat all URLs as opaque then you will be isolated

from implementation changes as the HornetQ REST interface evolves over time.

Chapter 3. HornetQ REST Inter...

10

3.2. Queue Resource Response Headers

Below is a list of response headers you should expect when interacting with a Queue resource.

msg-create

This is a URL you POST messages to. The semantics of this link are described in Chapter 4.

msg-create-with-id

This is a URL template you POST message to. The semantics of this link are described in

Chapter 4.

msg-pull-consumers

This is a URL for creating consumers that will pull from a queue. The semantics of this link

are described in Chapter 5.

msg-push-consumers

This is a URL for registering other URLs you want the HornetQ REST server to push messages

to. The semantics of this link are described in Chapter 6

3.3. Topic Resource Respones Headers

Below is a list of response headers you should expect when interacting with a Topic resource.

msg-create

This is a URL you POST messages to. The semantics of this link are described in Chapter 4.

msg-create-with-id

This is a URL template you POST messages to. The semantics of this link are described in

Chapter 4.

msg-pull-subscriptions

This is a URL for creating subscribers that will pull from a topic. The semantics of this link

are described in Chapter 5.

msg-push-subscriptions

This is a URL for registering other URLs you want the HornetQ REST server to push messages

to. The semantics of this link are described in Chapter 6.

Chapter 4.

11

Posting MessagesThis chapter discusses the protocol for posting messages to a queue or a topic. In Chapter 3,

you saw that a queue or topic resource publishes variable custom headers that are links to other

RESTful resources. The msg-create header is the URL you post messages to. Messages are

published to a queue or topic by sending a simple HTTP message to the URL published by the

msg-create header. The HTTP message contains whatever content you want to publish to the

HornetQ destination. Here's an example scenario:

1. Obtain the starting msg-create header from the queue or topic resource.


Host: example.com

--- Response ---

HTTP/1.1 200 Ok


msg-create-with-id: http://example.com/queues/jms.queue.bar/create/{id}

2. Do a POST to the URL contained in the msg-create header.

POST /queues/jms.queue.bar/create

Host: example.com


<order>

<name>Bill</name>

<item>iPhone4</name>


</order>

--- Response ---

HTTP/1.1 201 Created

msg-create-next: http://example.com/queues/jms.queue.bar/create/002

A successful response will return a 201 response code. Also notice that a msg-create-next

response header is sent as well. You must use this URL to POST your next message.

3. POST your next message to the queue using the URL returned in the msg-create-next

header.

Chapter 4. Posting Messages

12

POST /queues/jms.queue.bar/create/002

Host: example.com


<order>

<name>Monica</name>

<item>iPad</item>


</order>

--- Response --



Continue using the new msg-create-next header returned with each response.

It is VERY IMPORTENT that you never re-use returned msg-create-next headers to post new

messages. This URL may be uniquely generated for each message and used for duplicate

detection. If you lose the URL within the msg-create-next header, then just go back to the queue

or topic resource to get the msg-create URL.

4.1. Duplicate Detection

Sometimes you might have network problems when posting new messages to a queue or topic.

You may do a POST and never receive a response. Unfortunately, you don't know whether or

not the server received the message and so a re-post of the message might cause duplicates to

be posted to the queue or topic. By default, the HornetQ REST interface is configured to accept

and post duplicate messages. You can change this by turning on duplicate message detection

by setting the dups-ok config option to false as described in Chapter 3. When you do this, the

initial POST to the msg-create URL will redirect you, using the standard HTTP 307 redirection

mechanism to a unique URL to POST to. All other interactions remain the same as discussed

earlier. Here's an example:

1. Obtain the starting msg-create header from the queue or topic resource.


Host: example.com

--- Response ---

HTTP/1.1 200 Ok



Duplicate Detection

13

2. Do a POST to the URL contained in the msg-create header.

POST /queues/jms.queue.bar/create

Host: example.com


<order>

<name>Bill</name>



</order>

--- Response ---

HTTP/1.1 307 Redirect

Location: http://example.com/queues/jms.queue.bar/create/001

A successful response will return a 307 response code. This is standard HTTP protocol. It is

telling you that you must re-POST to the URL contained within the Location header.

3. re-POST your message to the URL provided within the Location header.


Host: example.com


<order>

<name>Bill</name>



</order>

--- Response --



You should receive a 201 Created response. If there is a network failure, just re-POST to the

Location header. For new messages, use the returned msg-create-next header returned with

each response.

4. POST any new message to the returned msg-create-next header.


Chapter 4. Posting Messages

14

Host: example.com


<order>

<name>Monica</name>

<item>iPad</name>


</order>

--- Response --



If there ever is a network problem, just repost to the URL provided in the msg-create-next

header.

How can this work? As you can see, with each successful response, the HornetQ REST server

returns a uniquely generated URL within the msg-create-next header. This URL is dedicated to the

next new message you want to post. Behind the scenes, the code extracts an identify from the URL

and uses HornetQ's duplicate detection mechanism by setting the DUPLICATE_DETECTION_ID

property of the JMS message that is actually posted to the system.

An alternative to this approach is to use the msg-create-with-id header. This is not an invokable

URL, but a URL template. The idea is that the client provides the DUPLICATE_DETECTION_ID and

creates it's own create-next URL. The msg-create-with-id header looks like this (you've see

it in previous examples, but we haven't used it):


You see that it is a regular URL appended with a {id}. This {id} is a pattern matching substring.

A client would generate its DUPLICATE_DETECTION_ID and replace {id} with that generated id,

then POST to the new URL. The URL the client creates works exactly like a create-next URL

described earlier. The response of this POST would also return a new msg-create-next header.

The client can continue to generate its own DUPLICATE_DETECTION_ID, or use the new URL

returned via the msg-create-next header.

The advantage of this approach is that the client does not have to repost the message. It also only

has to come up with a unique DUPLICATE_DETECTION_ID once.

4.2. Persistent Messages

By default, posted messages are not durable and will not be persisted in HornetQ's journal. You

can create durable messages by modifying the default configuration as expressed in Chapter 2

so that all messages are persisted when sent. Alternatively, you can set a URL query parameter

TTL, Expiration and Priority

15

called durable to true when you post your messages to the URLs returned in the msg-create,

msg-create-with-id, or msg-create-next headers. here's an example of that.

POST /queues/jms.queue.bar/create?durable=true

Host: example.com


<order>

<name>Bill</name>

<item>iPhone4</item>


</order>

4.3. TTL, Expiration and Priority

You can set the time to live, expiration, and/or the priority of the message in the queue or topic

by setting an additional query parameter. The expiration query parameter is an long specify the

time in milliseconds since epoch (a long date). The ttl query parameter is a time in milliseconds

you want the message active. The priority is another query parameter with an integer value

between 0 and 9 expressing the priority of the message. i.e.:

POST /queues/jms.queue.bar/create?expiration=30000&priority=3

Host: example.com


<order>

<name>Bill</name>

<item>iPhone4</item>


</order>

Chapter 5.

17

Consuming Messages via PullThere are two different ways to consume messages from a topic or queue. You can wait and

have the messaging server push them to you, or you can continuously poll the server yourself to

see if messages are available. This chapter discusses the latter. Consuming messages via a pull

works almost identically for queues and topics with some minor, but important caveats. To start

consuming you must create a consumer resource on the server that is dedicated to your client.

Now, this pretty much breaks the stateless principle of REST, but after much prototyping, this is

the best way to work most effectively with HornetQ through a REST interface.

You create consumer resources by doing a simple POST to the URL published by the msg-

pull-consumers response header if you're interacting with a queue, the msg-pull-subscribers

response header if you're interacting with a topic. These headers are provided by the main queue

or topic resource discussed in Chapter 3. Doing an empty POST to one of these URLs will create

a consumer resource that follows an auto-acknowledge protocol and, if you're interacting with

a topic, creates a temporty subscription to the topic. If you want to use the acknowledgement

protocol and/or create a durable subscription (topics only), then you must use the form parameters

(application/x-www-form-urlencoded) described below.

autoAck

A value of true or false can be given. This defaults to true if you do not pass this parameter.

durable

A value of true or false can be given. This defaults to false if you do not pass this parameter.

Only available on topics. This specifies whether you want a durable subscription or not. A

durable subscription persists through server restart.

name

This is the name of the durable subscription. If you do not provide this parameter, the name

will be automatically generated by the server. Only usable on topics.

selector

This is an optional JMS selector string. The HornetQ REST interface adds HTTP headers to

the JMS message for REST produced messages. HTTP headers are prefixed with "http_" and

every '-' charactor is converted to a '$'.

idle-timeout

For a topic subscription, idle time in milliseconds in which the consumer connections will be

closed if idle.

delete-when-idle

Boolean value, If true, a topic subscription will be deleted (even if it is durable) when an the

idle timeout is reached.

Chapter 5. Consuming Messages...

18

5.1. Auto-Acknowledge

This section focuses on the auto-acknowledge protocol for consuming messages via a pull. Here's

a list of the response headers and URLs you'll be interested in.

msg-pull-consumers

The URL of a factory resource for creating queue consumer resources. You will pull from

these created resources.


The URL of a factory resource for creating topic subscription resources. You will pull from the

created resources.

msg-consume-next

The URL you will pull the next message from. This is returned with every response.

msg-consumer

This is a URL pointing back to the consumer or subscription resource created for the client.

5.1.1. Creating an Auto-Ack Consumer or Subscription

Here is an example of creating an auto-acknowledged queue pull consumer.

1. Find the pull-consumers URL by doing a HEAD or GET request to the base queue resource.


Host: example.com

--- Response ---

HTTP/1.1 200 Ok




2. Next do an empty POST to the URL returned in the msg-pull-consumers header.

POST /queues/jms.queue.bar/pull-consumers HTTP/1.1

Host: example.com

--- response ---


Location: http://example.com/queues/jms.queue.bar/pull-consumers/auto-ack/333

msg-consume-next: http://example.com/queues/jms.queue.bar/pull-consumers/auto-ack/333/

consume-next-1

Consuming Messages

19

The Location header points to the JMS consumer resource that was created on the server. It

is good to remember this URL, although, as you'll see later, it is transmitted with each response

just to remind you.

Creating an auto-acknowledged consumer for a topic is pretty much the same. Here's an example

of creating a durable auto-acknowledged topic pull subscription.

1. Find the pull-subscriptions URL by doing a HEAD or GET request to the base topic

resource

HEAD /topics/jms.topic.bar HTTP/1.1

Host: example.com

--- Response ---

HTTP/1.1 200 Ok

msg-create: http://example.com/topics/jms.topic.foo/create

msg-pull-subscriptions: http://example.com/topics/jms.topic.foo/pull-subscriptions

msg-push-subscriptions: http://example.com/topics/jms.topic.foo/push-subscriptions

2. Next do a POST to the URL returned in the msg-pull-subscriptions header passing in a

true value for the durable form parameter.

POST /topics/jms.topic.foo/pull-subscriptions HTTP/1.1

Host: example.com

Content-Type: application/x-www-form-urlencoded

durable=true

--- Response ---


Location: http://example.com/topics/jms.topic.foo/pull-subscriptions/auto-ack/222

msg-consume-next: http://example.com/topics/jms.topic.foo/pull-subscriptions/auto-ack/222/

consume-next-1

The Location header points to the JMS subscription resource that was created on the server. It


just to remind you.

5.1.2. Consuming Messages

After you have created a consumer resource, you are ready to start pulling messages from the

server. Notice that when you created the consumer for either the queue or topic, the response


20

contained a msg-consume-next response header. POST to the URL contained within this header

to consume the next message in the queue or topic subscription. A successful POST causes the

server to extract a message from the queue or topic subscription, acknowledge it, and return it to

the consuming client. If there are no messages in the queue or topic subscription, a 503 (Service

Unavailable) HTTP code is returned.

Warning

For both successful and unsuccessful posts to the msg-consume-next URL, the

response will contain a new msg-consume-next header. You must ALWAYS use

this new URL returned within the new msg-consume-next header to consume new

messages.

Here's an example of pulling multiple messages from the consumer resource.

1. Do a POST on the msg-consume-next URL that was returned with the consumer or subscription

resource discussed earlier.

POST /queues/jms.queue.bar/pull-consumers/consume-next-1

Host: example.com

--- Response ---

HTTP/1.1 200 Ok


msg-consume-next: http://example.com/queues/jms.queue.bar/pull-consumers/333/consume-

next-2

msg-consumer: http://example.com/queues/jms.queue.bar/pull-consumers/333

<order>...</order>

The POST returns the message consumed from the queue. It also returns a new msg-consume-

next link. Use this new link to get the next message. Notice also a msg-consumer response

header is returned. This is a URL that points back to the consumer or subscription resource.

You will need that to clean up your connection after you are finished using the queue or topic.

2. The POST returns the message consumed from the queue. It also returns a new msg-consume-

next link. Use this new link to get the next message.


Host: example.com

--- Response ---

Recovering From Network Failures

21

Http/1.1 503 Service Unavailable

Retry-After: 5


next-2

In this case, there are no messages in the queue, so we get a 503 response back. As per the

HTTP 1.1 spec, a 503 response may return a Retry-After head specifying the time in seconds

that you should retry a post. Also notice, that another new msg-consume-next URL is present.

Although it probabley is the same URL you used last post, get in the habit of using URLs

returned in response headers as future versions of HornetQ REST might be redirecting you or

adding additional data to the URL after timeouts like this.

3. POST to the URL within the last msg-consume-next to get the next message.


Host: example.com

--- Response ---

HTTP/1.1 200 Ok



next-3

<order>...</order>

5.1.3. Recovering From Network Failures

If you experience a network failure and do not know if your post to a msg-consume-next URL was

successful or not, just re-do your POST. A POST to a msg-consume-next URL is idempotent,

meaning that it will return the same result if you execute on any one msg-consume-next URL more

than once. Behind the scenes, the consumer resource caches the last consumed message so

that if there is a message failure and you do a re-post, the cached last message will be returned

(along with a new msg-consume-next URL). This is the reason why the protocol always requires

you to use the next new msg-consume-next URL returned with each response. Information about

what state the client is in is embedded within the actual URL.

5.1.4. Recovering From Client or Server Crashes

If the server crashes and you do a POST to the msg-consume-next URL, the server will return a

412 (Preconditions Failed) response code. This is telling you that the URL you are using is out of

sync with the server. The response will contain a new msg-consume-next header to invoke on.

If the client crashes there are multiple ways you can recover. If you have remembered the last msg-

consume-next link, you can just re-POST to it. If you have remembered the consumer resource


22

URL, you can do a GET or HEAD request to obtain a new msg-consume-next URL. If you have

created a topic subscription using the name parameter discussed earlier, you can re-create the

consumer. Re-creation will return a msg-consume-next URL you can use. If you cannot do any of

these things, you will have to create a new consumer.

The problem with the auto-acknowledge protocol is that if the client or server crashes, it is

possible for you to skip messages. The scenario would happen if the server crashes after auto-

acknowledging a message and before the client receives the message. If you want more reliable

messaging, then you must use the acknowledgement protocol.

5.2. Manual Acknowledgement

The manual acknowledgement protocol is similar to the auto-ack protocol except there is an

additional round trip to the server to tell it that you have received the message and that the server

can internally ack the message. Here is a list of the respone headers you will be interested in.

msg-pull-consumers

The URL of a factory resource for creating queue consumer resources. You will pull from

these created resources


The URL of a factory resource for creating topic subscription resources. You will pull from the

created resources.

msg-acknowledge-next

URL used to obtain the next message in the queue or topic subscription. It does not

acknowledge the message though.

msg-acknowledgement

URL used to acknowledge a message.

msg-consumer

This is a URL pointing back to the consumer or subscription resource created for the client.

5.2.1. Creating manually-acknowledged consumers or

subscriptions

Here is an example of creating an auto-acknowledged queue pull consumer.

1. Find the pull-consumers URL by doing a HEAD or GET request to the base queue resource.


Host: example.com

Creating manually-acknowledged consumers or

subscriptions

23

--- Response ---

HTTP/1.1 200 Ok




2. Next do a POST to the URL returned in the msg-pull-consumers header passing in a false

value to the autoAck form parameter .

POST /queues/jms.queue.bar/pull-consumers HTTP/1.1

Host: example.com


autoAck=false

--- response ---


Location: http://example.com/queues/jms.queue.bar/pull-consumers/acknowledged/333

msg-acknowledge-next: http://example.com/queues/jms.queue.bar/pull-consumers/

acknowledged/333/acknowledge-next-1

The Location header points to the JMS consumer resource that was created on the server. It


just to remind you.

Creating an manually-acknowledged consumer for a topic is pretty much the same. Here's an

example of creating a durable manually-acknowledged topic pull subscription.

1. Find the pull-subscriptions URL by doing a HEAD or GET request to the base topic

resource


Host: example.com

--- Response ---

HTTP/1.1 200 Ok

msg-create: http://example.com/topics/jms.topic.foo/create

msg-pull-subscriptions: http://example.com/topics/jms.topic.foo/pull-subscriptions

msg-push-subscriptions: http://example.com/topics/jms.topic.foo/push-subscriptions

2. Next do a POST to the URL returned in the msg-pull-subscriptions header passing in a

true value for the durable form parameter and a false value to the autoAck form parameter.


24

POST /topics/jms.topic.foo/pull-subscriptions HTTP/1.1

Host: example.com


durable=true&autoAck=false

--- Response ---


Location: http://example.com/topics/jms.topic.foo/pull-subscriptions/acknowledged/222

msg-acknowledge-next: http://example.com/topics/jms.topic.foo/pull-subscriptions/

acknowledged/222/consume-next-1

The Location header points to the JMS subscription resource that was created on the server. It


just to remind you.

5.2.2. Consuming and Acknowledging a Message

After you have created a consumer resource, you are ready to start pulling messages from the

server. Notice that when you created the consumer for either the queue or topic, the response

contained a msg-acknowledge-next response header. POST to the URL contained within this

header to consume the next message in the queue or topic subscription. If there are no messages

in the queue or topic subscription, a 503 (Service Unavailable) HTTP code is returned. A

successful POST causes the server to extract a message from the queue or topic subscription

and return it to the consuming client. It does not acknowledge the message though. The response

will contain the acknowledgement header which you will use to acknowledge the message.

Here's an example of pulling multiple messages from the consumer resource.

1. Do a POST on the msg-acknowledge-next URL that was returned with the consumer or

subscription resource discussed earlier.


Host: example.com

--- Response ---

HTTP/1.1 200 Ok


msg-acknowledgement: http://example.com/queues/jms.queue.bar/pull-consumers/333/

acknowledgement/2

msg-consumer: http://example.com/queues/jms.queue.bar/pull-consumers/333

Recovering From Network Failures

25

<order>...</order>

The POST returns the message consumed from the queue. It also returns a msg-

acknowledgement link. You will use this new link to acknowledge the message. Notice also a

msg-consumer response header is returned. This is a URL that points back to the consumer

or subscription resource. You will need that to clean up your connection after you are finished

using the queue or topic.

2. Acknowledge or unacknowledge the message by doing a POST to the URL contained in the

msg-acknowledgement header. You must pass an acknowledge form parameter set to true

or false depending on whether you want to acknowledge or unacknowledge the message on

the server.

POST /queues/jms.queue.bar/pull-consumers/acknowledgement/2

Host: example.com


acknowledge=true

--- Response ---

Http/1.1 200 Ok

msg-acknowledge-next: http://example.com/queues/jms.queue.bar/pull-consumers/333/

acknowledge-next-2

Whether you acknowledge or unacknowledge the message, the response will contain a new

msg-acknowledge-next header that you must use to obtain the next message.

5.2.3. Recovering From Network Failures

If you experience a network failure and do not know if your post to a msg-acknowledge-next

or msg-acknowledgement URL was successful or not, just re-do your POST. A POST to one

of these URLs is idempotent, meaning that it will return the same result if you re-post. Behind

the scenes, the consumer resource keeps track of its current state. If the last action was a call

to msg-acknowledge-next, it will have the last message cached, so that if a re-post is done, it

will return the message again. Same goes with re-posting to msg-acknowledgement. The server

remembers its last state and will return the same results. If you look at the URLs you'll see that

they contain information about the expected current state of the server. This is how the server

knows what the client is expecting.

5.2.4. Recovering From Client or Server Crashes

If the server crashes and while you are doing a POST to the msg-acknowledge-next URL, just

re-post. Everything should reconnect all right. On the other hand, if the server crashes while you

are doing a POST to msg-acknowledgement, the server will return a 412 (Preconditions Failed)


26

response code. This is telling you that the URL you are using is out of sync with the server and

the message you are acknowledging was probably re-enqueued. The response will contain a new

msg-acknowledge-next header to invoke on.

As long as you have "bookmarked" the consumer resource URL (returned from Location header

on a create, or the msg-consumer header), you can recover from client crashes by doing a GET or

HEAD request on the consumer resource to obtain what state you are in. If the consumer resource

is expecting you to acknowledge a message, it will return a msg-acknowledgement header in

the response. If the consumer resource is expecting you to pull for the next message, the msg-

acknowledge-next header will be in the response. With manual acknowledgement you are pretty

much guaranteed to avoid skipped messages. For topic subscriptions that were created with a

name parameter, you do not have to "bookmark" the returned URL. Instead, you can re-create the

consumer resource with the same exact name. The response will contain the same information

as if you did a GET or HEAD request on the consumer resource.

5.3. Blocking Pulls with Accept-Wait

Unless your queue or topic has a high rate of message flowing though it, if you use the pull

protocol, you're going to be receiving a lot of 503 responses as you continuously pull the server for

new messages. To alleviate this problem, the HornetQ REST interface provides the Accept-Wait

header. This is a generic HTTP request header that is a hint to the server for how long the client is

willing to wait for a response from the server. The value of this header is the time in seconds the

client is willing to block for. You would send this request header with your pull requests. Here's

an example:


Host: example.com

Accept-Wait: 30

--- Response ---

HTTP/1.1 200 Ok



next-3

<order>...</order>

In this example, we're posting to a msg-consume-next URL and telling the server that we would

be willing to block for 30 seconds.

5.4. Clean Up Your Consumers!

When the client is done with its consumer or topic subscription it should do an HTTP DELETE

call on the consumer URL passed back from the Location header or the msg-consumer response

Clean Up Your Consumers!

27

header. The server will time out a consumer with the value configured from Chapter 2.3, so you

don't have to clean up if you dont' want to, but if you are a good kid, you will clean up your

messes. A consumer timeout for durable subscriptions will not delete the underlying durable JMS

subscription though, only the server-side consumer resource (and underlying JMS session).

Chapter 6.

29

Pushing MessagesYou can configure the HornetQ REST server to push messages to a registered URL either

remotely through the REST interface, or by creating a pre-configured XML file for the HornetQ

REST server to load at boot time.

6.1. The Queue Push Subscription XML

Creating a push consumer for a queue first involves creating a very simple XML document. This

document tells the server if the push subscription should survive server reboots (is it durable). It

must provide a URL to ship the forwarded message to. Finally, you have to provide authentication

information if the final endpoint requires authentication. Here's a simple example:

<push-registration>

<durable>false</durable>

<selector><![CDATA[

SomeAttribute > 1

]]>

</selector>

<link rel="push" href="http://somewhere.com" type="application/json" method="PUT"/>

<maxRetries>5</maxRetries>

<retryWaitMillis>1000</retryWaitMillis>

<disableOnFailure>true</disableOnFailure>

</push-registration>

The durable element specifies whether the registration should be saved to disk so that if there

is a server restart, the push subscription will still work. This element is not required. If left out it

defaults to false. If durable is set to true, an XML file for the push subscription will be created

within the directory specified by the queue-push-store-dir config variable defined in Chapter

2. (topic-push-store-dir for topics).

The selector element is optional and defines a JMS message selector. You should enclose it

within CDATA blocks as some of the selector characters are illegal XML.

The maxRetries element specifies how many times a the server will try to push a message to a

URL if there is a connection failure.

The retryWaitMillis element specifies how long to wait before performing a retry.

The disableOnFailure element, if set to true, will disable the registration if all retries have failed.

It will not disable the connection on non-connection-failure issues (like a bad request for instance).

In these cases, the dead letter queue logic of HornetQ will take over.

The link element specifies the basis of the interaction. The href attribute contains the URL you

want to interact with. It is the only required attribute. The type attribute specifies the content-type

Chapter 6. Pushing Messages

30

ofwhat the push URL is expecting. The method attribute defines what HTTP method the server

will use when it sends the message to the server. If it is not provided it defaults to POST. The

rel attribute is very important and the value of it triggers different behavior. Here's the values a

rel attribute can have:

destination

The href URL is assumed to be a queue or topic resource of another HornetQ REST server.

The push registration will initially do a HEAD request to this URL to obtain a msg-create-with-id

header. It will use this header to push new messages to the HornetQ REST endpoint reliably.

Here's an example:

<push-registration>

<link rel="destination" href="http://somewhere.com/queues/jms.queue.foo"/>


template

In this case, the server is expecting the link element's href attribute to be a URL expression.

The URL expression must have one and only one URL parameter within it. The server will

use a unique value to create the endpoint URL. Here's an example:

<push-registration>

<link rel="template" href="http://somewhere.com/resources/{id}/messages" method="PUT"/

>


In this example, the {id} sub-string is the one and only one URL parameter.

user defined

If the rel attributes is not destination or template (or is empty or missing), then the server

will send an HTTP message to the href URL using the HTTP method defined in the method

attribute. Here's an example:

<push-registration>

<link href="http://somewhere.com" type="application/json" method="PUT"/>


6.2. The Topic Push Subscription XML

The push XML for a topic is the same except the root element is push-topic-registration. (Also

remember the selector element is optional). The rest of the document is the same. Here's an

example of a template registration:

Creating a Push Subscription at Runtime

31

<push-topic-registration>

<durable>true</durable>

<selector><![CDATA[

SomeAttribute > 1

]]>

</selector>

<link rel="template" href="http://somewhere.com/resources/{id}/messages" method="POST"/>

</push-topic registration>

6.3. Creating a Push Subscription at Runtime

Creating a push subscription at runtime involves getting the factory resource URL from the msg-

push-consumers header, if the destination is a queue, or msg-push-subscriptions header, if the

destination is a topic. Here's an example of creating a push registration for a queue:

1. First do a HEAD request to the queue resource:


Host: example.com

--- Response ---

HTTP/1.1 200 Ok




2. Next POST your subscription XML to the URL returned from msg-push-consumers header

POST /queues/jms.queue.bar/push-consumers

Host: example.com


<push-registration>

<link rel="destination" href="http://somewhere.com/queues/jms.queue.foo"/>


--- Response ---


Location: http://example.com/queues/jms.queue.bar/push-consumers/1-333-1212


32

The Location header contains the URL for the created resource. If you want to unregister this,

then do a HTTP DELETE on this URL.

Here's an example of creating a push registration for a topic:

1. First do a HEAD request to the topic resource:


Host: example.com

--- Response ---

HTTP/1.1 200 Ok

msg-create: http://example.com/topics/jms.topic.bar/create

msg-pull-subscriptions: http://example.com/topics/jms.topic.bar/pull-subscriptions

msg-push-subscriptions: http://example.com/topics/jms.topic.bar/push-subscriptions

2. Next POST your subscription XML to the URL returned from msg-push-subscriptions header

POST /topics/jms.topic.bar/push-subscriptions

Host: example.com


<push-registration>

<link rel="template" href="http://somewhere.com/resources/{id}"/>


--- Response ---


Location: http://example.com/topics/jms.topic.bar/push-subscriptions/1-333-1212

The Location header contains the URL for the created resource. If you want to unregister this,

then do a HTTP DELETE on this URL.

6.4. Creating a Push Subscription by Hand

You can create a push XML file yourself if you do not want to go through the REST interface

to create a push subscription. There is some additional information you need to provide though.

First, in the root element, you must define a unique id attribute. You must also define a destination

element to specify the queue you should register a consumer with. For a topic, the destination

element is the name of the subscription that will be reated. For a topic, you must also specify the

topic name within the topic element.

Pushing to Authenticated Servers

33

Here's an example of a hand-created queue registration. This file must go in the directory specified

by the queue-push-store-dir config variable defined in Chapter 2:

<push-registration id="111">

<destination>jms.queue.bar</destination>

<durable>true>

<link rel="template" href="http://somewhere.com/resources/{id}/messages" method="PUT"/>


Here's an example of a hand-created topic registration. This file must go in the directory specified

by the topic-push-store-dir config variable defined in Chapter 2:

<push-topic-registration id="112">

<destination>my-subscription-1</destination


<link rel="template" href="http://somewhere.com/resources/{id}/messages" method="PUT"/>

<topic>jms.topic.foo</topic>

</push-topic-registration>

6.5. Pushing to Authenticated Servers

Push subscriptions only support BASIC and DIGEST authentication out of the box. Here is an

example of adding BASIC authentication:




<authentication>

<basic-auth>

<username>guest</username>

<password>geheim</password>

</basic-auth>

</authentication>


For DIGEST, just replace basic-auth with digest-auth.

For other authentication mechanisms, you can register headers you want transmitted with each

request. Use the header element with the name attribute representing the name of the header.

Here's what custom headers might look like:


34




<header name="secret-header">jfdiwe3321</header>


Chapter 7.

35

Creating DestinationsYou can create a durable queue or topic through the REST interface. Currently you cannot create

a temporary queue or topic. To create a queue you do a POST to the relative URL /queues with

an XML representation of the queue. The XML syntax is the same queue syntax that you would

specify in hornetq-jms.xml if you were creating a queue there. For example:

POST /queues

Host: example.com

Content-Type: application/hornetq.jms.queue+xml

<queue name="testQueue">


</queue>

--- Response ---


Location: http://example.com/queues/jms.queue.testQueue

Notice that the Content-Type is application/hornetq.jms.queue+xml.

Here's what creating a topic would look like:

POST /topics

Host: example.com

Content-Type: application/hornetq.jms.topic+xml

<topic name="testTopic">

</topic>

--- Response ---


Location: http://example.com/topics/jms.topic.testTopic

Chapter 8.

37

Securing the HornetQ REST

Interface

8.1. Within JBoss Application server

Securing the HornetQ REST interface is very simple with the JBoss Application Server. You turn

on authentication for all URLs within your WAR's web.xml, and let the user Principal to propagate

to HornetQ. This only works if you are using the JBossSecurityManager with HornetQ. See the

HornetQ documentation for more details.

8.2. Security in other environments

To secure the HornetQ REST interface in other environments you must role your own security

by specifying security constraints with your web.xml for every path of every queue and topic you

have deployed. Here is a list of URI patterns:

Table 8.1.

/queues secure the POST operation to secure queue

creation

/queues/{queue-name} secure the GET HEAD operation to getting

information about the queue.

/queues/{queue-name}/create/* secure this URL pattern for producing

messages.

/queues/{queue-name}/pull-consumers/* secure this URL pattern for pulling messages

messages.

/queues/{queue-name}/push-consumers/* secure this URL pattern for pushing messages.

/topics secure the POST operation to secure topic

creation

/topics/{topic-name} secure the GET HEAD operation to getting

information about the topic.

/topics/{topic-name}/create/* secure this URL pattern for producing

messages.

/topics/{topic-name}/pull-subscriptions/* secure this URL pattern for pulling messages

messages.

/topics/{topic-name}/push-subscriptions/* secure this URL pattern for pushing messages.

Chapter 9.

39

Mixing JMS and RESTThe HornetQ REST interface supports mixing JMS and REST producres and consumers. You

can send an ObjectMessage through a JMS Producer, and have a REST client consume it. You

can have a REST client POST a message to a topic and have a JMS Consumer receive it. Some

simple transformations are supported if you have the correct RESTEasy providers installed.

9.1. JMS Producers - REST Consumers

If you have a JMS producer, the HornetQ REST interface only supports ObjectMessage type. If

the JMS producer is aware that there may be REST consumers, it should set a JMS property to

specify what Content-Type the Java object should be translated into by REST clients. The HornetQ

REST server will use RESTEasy content handlers (MessageBodyReader/Writers) to transform

the Java object to the type desired. Here's an example of a JMS producer setting the content

type of the message.

ObjectMessage message = session.createObjectMessage();

message.setStringProperty(org.hornetq.rest.HttpHeaderProperty.CONTENT_TYPE,

"application/xml");

If the JMS producer does not set the content-type, then this information must be obtained from

the REST consumer. If it is a pull consumer, then the REST client should send an Accept header

with the desired media types it wants to convert the Java object into. If the REST client is a push

registration, then the type attribute of the link element of the push registration should be set to

the desired type.

9.2. REST Producers - JMS Consumers

If you have a REST client producing messages and a JMS consumer, HornetQ REST has a simple

helper class for you to transform the HTTP body to a Java object. Here's some example code:

public void onMessage(Message message)

{

MyType obj = org.hornetq.rest.Jms.getEntity(message, MyType.class);

}

The way the getEntity() method works is that if the message is an ObjectMessage, it will try to

extract the desired type from it like any other JMS message. If a REST producer sent the message,

then the method uses RESTEasy to convert the HTTP body to the Java object you want. See the

Javadoc of this class for more helper methods.

2.2 - community driven open source middleware

Documents